Key Winemaking Techniques
Malolactic fermentation, lees ageing, oak, and other winemaking decisions that shape wine style
Learning Objectives
- Explain what malolactic fermentation is and its effect on wine style
- Describe the effects of lees contact and bâtonnage on white wine
- Explain how oak use (new vs old, French vs American) shapes wine character
- Link specific winemaking decisions to their intended stylistic outcomes
Malolactic Fermentation (MLF)
Malolactic fermentation (MLF) is a bacterial conversion of sharp malic acid (think green apple) into softer lactic acid (think milk). Unlike alcoholic fermentation, MLF does not significantly increase alcohol — its purpose is to reduce acidity and add textural complexity. MLF also produces diacetyl, which gives wines a buttery or creamy character. It is almost always carried out in red wines, as it softens the wine and increases microbial stability. For white wines, the winemaker chooses: Burgundy Chardonnay typically undergoes MLF for richness; Chablis and most Sauvignon Blanc are blocked from MLF to preserve freshness.
Lees Contact and Bâtonnage
After fermentation, the dead yeast cells (lees) settle at the bottom of the tank or barrel. Extended contact with lees (sur lie ageing) adds creaminess, texture, and complexity — in Muscadet, legal minimum lees contact time is specified on the label (Muscadet Sèvre et Maine sur lie). In barrel-aged white wines, the winemaker may periodically stir the lees (bâtonnage) to keep them in suspension, enhancing their flavour contribution and adding a richer, more oily texture. Excessive bâtonnage can create a reductive environment, potentially causing off-aromas.
Oak — Vessels, Age, and Toast
Oak barrels impart flavour, controlled oxygenation, and structure. New French oak barriques (225L) add the most flavour — vanilla, toast, spice — and are preferred for premium Chardonnay and red wines. With each use, the barrel contributes less flavour; after 3–4 uses, it is effectively neutral for flavour but still provides micro-oxygenation. American oak has wider grain and imparts stronger, sweeter characters (coconut, dill). Toast level (light, medium, heavy) determines the character of the influence. Alternatives to barrel ageing include oak staves, chips, and inner staves — cheaper but less effective for quality wines.
Cold Stabilisation and Fining
Before bottling, most commercial wines undergo cold stabilisation (chilling to -4°C to precipitate tartrate crystals) and fining (adding clarifying agents such as bentonite clay, egg white, or isinglass that attract and precipitate particles). Fining agents that are animal-derived (egg white, isinglass, gelatine) require disclosure on labels in many markets and are avoided by vegan producers. Heavy fining and filtration can strip wine of character; minimal-intervention producers often avoid them entirely.
Key Vocabulary
Exam Question Examples
A winemaker decides to block malolactic fermentation in a Chardonnay. What stylistic effect does this have?
Approach
Blocking MLF preserves malic acid, maintaining higher total acidity and producing a crisper, fresher, more lean wine with green apple and citrus character rather than butter and cream. This is the approach used in Chablis and most unoaked Chardonnay to maximise freshness. Wines made this way are typically lower in alcohol (no alcohol is produced by MLF, but retained acidity makes wine taste lighter) and suit pairing with delicate seafood.
Quick Summary
- 1.MLF: sharp malic acid → soft lactic acid + buttery diacetyl; reduces acidity
- 2.MLF in reds: almost always done — softens wine, adds stability
- 3.MLF in whites: optional — adds richness (Burgundy Chardonnay) but reduces freshness
- 4.Lees ageing (sur lie): adds creaminess and complexity; bâtonnage stirs lees for more effect
- 5.New oak: vanilla, toast, spice; old oak: neutral for flavour, micro-oxygenation only
- 6.French oak: subtle, elegant; American oak: bolder, coconut/dill character
Practice questions on this topic
Frequently Asked Questions
- Does malolactic fermentation add alcohol to wine?
- No. MLF is carried out by bacteria (not yeast) and converts malic acid to lactic acid and CO₂. It does not produce significant quantities of alcohol. Its main effects are reducing acidity, softening texture, and adding buttery/creamy character from diacetyl production.
- What does "sur lie" mean on a Muscadet label?
- "Sur lie" means the wine has been aged on its lees (dead yeast cells) for a legally defined minimum period before bottling. For Muscadet Sèvre et Maine sur lie, minimum lees contact is until 1 March after the harvest. This adds a slight yeasty, creamy texture and complexity to what is otherwise a light, neutral wine.
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